The reiterative use of transcriptional regulatory factors is a hallmark of embryonic development. A relatively small number of proteins must mediate the multiplicity of cell fate decisions that pattern organs and organisms. The neural crest is an excellent system in which to examine the reiterative use of developmental regulatory proteins. SoxE factors are a key family of regulatory factors that mediate multiple cell fate decisions within the neural crest including the formation of the precursor population and differentiation of the melanocyte, cartilage and glial cell lineages. This makes SoxE proteins an important model for understanding the molecular mechanisms by which transcription factors can be repeatedly utilized to carry out diverse developmental roles, The goal of this research project is to investigate the roles that post-translational regulatory mechanisms such as SUMOylation, the differential utilization of SoxE protein domains, and interactions with other regulatory factors such as SoxD proteins and Wnt signals, play in the modulation of SoxE function. The foundation for this investigation has been laid by our studies demonstrating that SUMO modification of SoxE factors has a dramatic effect on their developmental function, switching them from promoters of neural crest formation to promoters of inner ear formation. We have built on these studies by demonstrating that SoxE factors are context dependent transcriptional regulators, and that SUMO modification converts them to repressors by facilitating the recruitment of groucho family co-repressors. We will use a combination of in vivo and in vitro approaches to further investigate the mechanisms via which SUMO modification alters SoxE function, as well as investigate how Wnt signals, SoxD factors, and specific SoxE functional domains contribute to the diverse functions of these factors. The proposed research is designed to reveal the molecular mechanisms that govern SoxE function and that may serve as paradigms for how other reiteratively utilized transcription factors can carry out such a diverse developmental of tasks. Because SoxE factors specifically, and the neural crest more generally, underlie a large group of diseases and congenital defects, this work will also directly impact issues related to human health. PUBLIC HEALTH RELEVANCE: The goal of this research project is to elucidate the molecular mechanisms via which Group E Sox factors are regulated, and to understand how this regulation contributes to their ability to control numerous distinct developmental decisions in the neural crest and other tissues. Both the neural crest and defects in SoxE proteins are linked to a number of human diseases and congenital disorders, and elucidating the molecular mechanisms regulating SoxE function is essential to understanding the pathogenesis of these disorders.